Every finish time from every race DUV records is sorted by distance, age group and gender. Enter yours and it finds where it sits in that order, so "a 12 hour 100K" becomes a position in a field of hundreds of thousands rather than a number on its own.

You get three comparisons: against everyone at that distance, against your own gender, and against your age group. They often differ more than people expect, which is usually the interesting part.